db buffer cache advisory clarification

Can anyone let me know why the advisory is saying i can so drastically reduce my PIO's by reducing my db_cache_size?

This was from a statspack 15 minute snap on 9.2.0.3

Buffer Pool Advisory for DB: MERLIN Instance: MERLIN End Snap: 24
-> Only rows with estimated physical reads >0 are displayed
-> ordered by Block Size, Buffers For Estimate

        Size for  Size  Buffers for  Est Physical          Estimated
P   Estimate (M) Factr     Estimate   Read Factor     Physical Reads
--- ------------ ----- ------------ ------------- ------------------
D             16    .3        1,985          0.06         76,733,864
D             32    .5        3,970          0.03         42,372,246
D             48    .8        5,955          0.01         14,388,875
D             64   1.0        7,940          1.00      1,235,406,218
D             80   1.3        9,925          0.99      1,218,140,869
D             96   1.5       11,910          0.97      1,202,045,787
D            112   1.8       13,895          0.96      1,186,037,878
D            128   2.0       15,880          0.95      1,170,539,124
D            144   2.3       17,865          0.93      1,153,082,843
D            160   2.5       19,850          0.92      1,136,840,124
D            176   2.8       21,835          0.91      1,120,406,916
D            192   3.0       23,820          0.89      1,105,315,871
D            208   3.3       25,805          0.88      1,091,342,049
D            224   3.5       27,790          0.87      1,078,433,638
D            240   3.8       29,775          0.86      1,066,281,869
D            256   4.0       31,760          0.85      1,055,056,082
D            272   4.3       33,745          0.85      1,044,234,271
D            288   4.5       35,730          0.84      1,032,099,896
D            304   4.8       37,715          0.82      1,014,564,963
D            320   5.0       39,700          0.79        973,654,538
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